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53 Cards in this Set

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What is a seizure
Excessive and/or hypersynchronous abnormal activity in the brain
What is epilepsy?
A disorder where the seizures are chronic and recurrent.
What is a convulsion?
Uncontrolled contractions of voluntary muscles.
Give some examples of possible positive and negative symptoms of a seizure.
Positive - jerking of a limb
Negative - amnesia
What percentage of the human population may be affected by seizures?
0.5 to 1%
What is the meaning of paroxysmal?
A sudden, sharp electrical event, e.g. a paroxysmal deporlarization shift.
What is the meaning of ictal?
A full seizure event. From the latin work ictus = strike.
What is the meaning of interictal?
Between seizures, usually refers to time.
What is an interictal "spike" from an EEG point of view and when recorded from a single neuron?
A sharp wave in EEG lasting 50-150 msec. When recorded from a single neuron, also known as a "paroxysmal depolarization shift."
What is the meaning of postictal and what is its alternate name?
Period after a seizure. Usually called postictal depression.
Why is the postictal period sometimes called the postictal depression?
Patients appear lethargic, confused or restless. Can be seconds to hours.
What is an aura?
Awareness or conscious sensation that precedes onset of certain types of seizures, e.g. strange odor, intense fear.
What are automatisms?
Stereotyped, involuntary motor activities, e.g. lip smaching, that often precede a seizure.
What are the two basic types of seizures?
Partial and generalized.
Where do partial seizures begin in the brain? What is an alternate name for these?
Begin in a focal cortical area, i.e. "focus" or epileptogenic zone. Often also called a "focal" seizure.
What are the two types of partial seizures?
Simple partial seizures and complex partial seizures.
What are the characteristics of simple partial seizures and what will be observed in an EEG?
Affect motor or sensory functions w/o disrupting consciousness. EEG seizure activity occurs in specific motor or sensor areas of neorcortex.
What are the characteristics of a complex partial seizures?
Consciousness lost or distrubed. Often begins with an aura and automatisms, and followed by amnesia and a period of confusion.
Where is a complex partial seizure likely to be located when viewing the EEG?
Often localized to temporal cortex.
What is an alternate name for complex partial seizures?
Psychomotor, temporal lobe or limbic seizures.
What is a generalized seizure?
Onsent is bilaterally symmetrical in the brain.
What are the two types of generalized seizures?
Non-convulsive and convulsive.
What is an older name for a non-convulsive generalized seizure?
petit mal
What age group are non-convulsive generalized seizures seen?
Children and adolsescents.
What is likely to be seen during a non-convulsive generalized seizure?
Last 2 to 10 seconds. Impaired consciousness associated wtih rolling of the eyes, blinking.
What is typically seen in an EEG with a non-convulsive generalized seizure?
Shows "3/sec spike and wave".
What are alternative names for a convulsive generalized seizure?
Grand mal or tonic-clonic.
What is likely to be observed during a convulsive generalized seizure?
Patients fall to the ground in rigid extension for 15-20 seconds (tonic phase), frequently loose bladder and bowel control. This blends into clonic phase: rhythmic limb contractions for 20-30 sec.
What will the EEG look like for a convulsive generalized seizure?
10-20 Hz high-ampltude activity during the tonic phase; groups of polyspikes separated by quiet intervals during clonic phase.
What could be an alternative outcome of a complex partial seizure?
Can spread bilaterally to cause a secondarily generalized seizure.
What is status epilepticus?
A medical emergency characterized by the recurrence of seizures at a rate so rapid that consciousness does not return to normal.
What is the epidemiology/causes of seizures?
Seizures can occur in normal brain - hypoxia, hypoglycemia, poisons, etc.
What is the epidemiology/causes of epilepsy?
Causes - Mechanisms unknown although know:
- Hereditary aspect - increased tendency for certain types of epilepsy
- Injury - head trauma, stroke, and turmors.
What are the basic mechamisms of seizure activity and epileptogenesis?
???
What are interictal discharges?
Paroxysmal depolarization shift (PDS) - sudden, large-amplitude and sustained deporlarization that is synchronized in many neurons (30 mv, 70-200 msec).
How can interictal discharges be experimentally induced?
By blocking synaptic inhibition and by other methods.
What are the mechanisms of synchrony?
Chemical synapses, electrical interactions, and ionic changes.
What are four cellular changes that are hypothesized to occur in epilepsy?
Less inhibition through loss of inhibitory interneurons?

Less inhibition through dormant inhibitory interneurons.

More synaptic excitation.

Synaptic reorganization - possible new recurrent excitatory circuits.
What are the two general approaches to controlling epilepsy?
Medication and resective surgery.
What are some of the antiepileptic druges (AEDs) and how do they work?
Barbituarates and benzodiazepines - augment GABA-mediated inhibition.

Phyenytoin - blocks high-frequency firing of action potentials.
Where is surgery most effective?
Primarily for intractable complex partial seizures in temporal lobe (hippocampus).
What is an EEG measuring?
They detect the synchronized activity of large numbers of cells; such signals are called field potentials. Because of the time scale - hundreds of ms - they do not measure action potentials per se.
What common cortical circuit results in an electrical response that is similar to a PDS (paraoxysmal depolarization shift)?
It is quite common to see a pyramidal cell with feedback through an inhibitory interneuron. Hence we will see an EPSP (depolarization) followed in time by an IPSP (hyperpolarization).
What are the two major stages in a paraoxysmal depolarization shift?
First, we see a sudden depolarization of the membrane potential that can last from 50 to 150 ms. At the end of this pulse will be a hyperpolarization wave.
What are the major channels involved in a paraoxysmal depolarization shift and its recovery?
Initially, AMPA channels will start the depolarization of the membrane. NMDA channels will typically turn on next (these are slower and last longer). There also may be voltage-gated calcium channels that turn on. One the feedback inhibitory circuit is activated, GABA-A channels will turn on in the pyramidal cell. There are often other K channels involved.
What are some of the things that can happen during a simple partial seizure?
Can be a clonic or tonic activity or a sensory perception, e.g. weird sensation.
What are some of the properties of complex partial seizures?
. Not so much where they occur
. Key - Disruption/loss of consciousness
. Learning/memory can occur (hippocampus) => amnesia
When do complex partial seizures often occur?
Going into or out of sleep.
What are two general properties of absence vs. tonic-clonic seizures? Concerns broad terms for times of stages.
short event/quick recovery vs. long event/slow recovery
What EEG phenomina is seen in most epileptic patients?
Interictal spikes
What is the effect of penicillin being introduced into the brain of a mouse?
Blocks GABA-A receptors => PDS and large EPSPs.
One mechanism of epilepsy relates to chemical synapses. What is happening?
Many pyramidal cells are interconnected. If inhibition stops => they can all fire at once.
One mechanism of epilepsy relates to electrical interaction. What does this mean?
Gap junctions tie together interneurons